Increasingly, owners of ageing dams are having to reconcile with the notion of involving others in decisions affecting the management of their dams. Previously recognised as ‘expert’ exclusive arenas, doctors, lawyers, scientists and engineers are now expected to respond to enquiring consumers and communities. Individuals and communities are expressing their need to share responsibilities.
Events at Hume Dam provide an illustration of the potential challenges and opportunities that all Dam Owners may face. This paper is a narrative of the processes of involving the wider ‘community’ in the Hume Dam remedial work project. It remains for the stakeholders to rate the effectiveness of the process.
Mark Foster, Robin Fell and Matt Spannagle
This paper describes a method for estimating the probability of failure of embankment dams by piping. The so called “UNSW method” is based on the results of an analysis of historic failures and accidents of embankment dams. An estimate of the probability of failure of a dam by piping is made by adjusting the historical rates of failure by piping by applying weighting factors which take into account the dam zoning; filters; age of the dam; core soil types; compaction; foundation geology; dam performance; and monitoring and surveillance. The method is intended for preliminary assessments only and is ideally suited as a risk ranking method for portfolio type risk assessments to identify which dams to prioritise for more detailed studies and as a check on event tree methods.
Alkali-aggregate reaction (AAR) is a potentially deleterious process in concrete containing reactive aggregates, and can lead to varying degrees of cracking in structures, and differential movement and misalignment of concrete elements and mechanical installations. The rehabilitation of affected structures would require information on the extent of current damage and possibility of on-going damage that could be caused by AAR.
Information on the characterisation of concrete components of an AAR-affected dam and estimation of their future potential for further expansion and cracking are provided and repair options discussed in this paper.
As New Zealand’s largest dam owner, ECNZ has actively managed dam safety since its inception in 1987. During this time it has managed several major dam safety issues and enhanced its dam safety management practices. This has occurred in an environment of organisational change and increasingly competitive commercial pressures.
The change in emphasis from a primarily technical emphasis to dam safety towards a commercial focus is described together with details of highly rated dam surveillance system, some continuous improvement initiatives, and recent enhancements to the dam safety programme. The position of responsible ownership in regard to risk and legal requirements is also discussed.
Trevor Daniell, David Kemp and Jenny Dickins
Early February 1997 saw the occurrence of heavy rainfalls over a wide area of South Australia’s north. One of the worst hit areas was near Olary, in eastern South Australia, where over a three day period, rainfall totals up to 320 mm were recorded. Within this period, localised, short duration intense rain occurred. In one four hour period on 7 February, about 200 mm fell.
The rain produced floods that washed away large sections of the main Sydney to Perth railway and inundated long sections of the Barrier Highway. Repair costs were of the order of $6 m for the railway and $1.5m for the road. Damage to rural infrastructure in the region was substantial. Flows within the catchment would have been sufficient to wash away most stream gauging stations.
The airmass over much of South Australia was of tropical origin, contained a high amount of moisture and was unstable. Thunderstorms were the main rain producer, consequently the event was characterised by localised, very intense rain episodes. This contrasts with the March 1989 floods, where it rained at a fairly steady rate over large areas for durations up to 24 hours, as a monsoon low tracked across the state.
Analysis of the depth-area relationship for the Olary storm indicates that the relationship to be used for design purposes should be the humid area relationship of Australian Rainfall and Runoff, not the arid area. This is reinforced when it is considered that the 1997 rainfall was localised, not general rain as in 1989.
Investigation of the event indicates that the Olary Creek catchment experienced overland flow, resulting in much higher peak flows than would occur with more frequently occurring “normal” processes. It is possible that any catchment may change its behaviour with extreme rainfall, and produce flows well in excess of those predicted with currently available runoff routing models, or flood frequency analysis of “normal” events.
A safety review of the Corin dam has identified several deficiencies including an inadequate spillway capacity. A hydraulic model test, included in the review indicated that the construction of a 1.3m wave wall along the top of the dam was required to prevent overtopping during the flood of 10,000 years.
The original post tensioning anchors installed along the spillway crest were also identified as unreliable due to inadequate corrosion protection measures.
This paper presents safety assessment and aspects of the construction of the remedial works for Corin Dam. As part of the safety review, the condition of the dam was reviewed against the risks of piping, slope instability, flood and seismic forces. The paper also discusses the long term effects of the acidic leakage on the grout curtain and on the integrity of the core.
The risk associated with the flooding during anchor installation and the discovery of a gap formation between the clay core and the concrete spillway wall are also considered.